Extending Array.prototype with "parallel" mappers and reducers.

js-array-parallel-map-reduce.js

Array.prototype.paraMap = function(...fns) {
  return fns.map(fn => this.map(fn))
}

Array.prototype.paraReduce = function(...fns) {
  let reduceArgs
  let init = fns[fns.length - 1]
  if (typeof init !== 'function') {
    reduceArgs = fns.slice(0, -1).map(fn => [fn, init])
  } else {
    reduceArgs = fns.map(fn => [fn])
  }
  return reduceArgs.map(args => Array.prototype.reduce.apply(this, args))
}

console.log([1, 2, 3].paraMap(
  (x => x % 3),
  (x => x * x),
  (x => -x)
))
// [ [ 1, 2, 0 ], [ 1, 4, 9 ], [ -1, -2, -3 ] ]

console.log([1, 2, 3].paraReduce(
  ((a, b) => a > b ? a : b), // max
  ((a, b) => a < b ? a : b) // min
))
// [ 3, 1 ]